1. Field of the Invention
The present invention relates to a method for preparing magnetite nanoparticles from low-grade iron ore using solvent extraction and magnetite nanoparticles prepared by the same.
2. Discussion of Related Art
Magnetite (Fe3O4) nanoparticles are suitable as a heavy metal adsorbent in wastewater treatment due to high heavy metal adsorption capacity, can be easily recovered after use due to excellent magnetic properties (Shipley, H. J., Yean, S., Kan, A. T., Tomson, M. B., Adsorption of arsenic to magnetite nanoparticles: Effect of particle concentration, pH, ionic strength, and temperature, Environ. Toxicol. Chem., 28, 509-15 (2009); de Vicente, I., Merino-Martos, A., Cruz-Pizarro, L., de Vicente, J., On the use of magnetic nano and microparticles for lake restoration, J. Hazard. Mater., 181, 375-81 (2010); Yuan, P., Liu, D., Fan, M., Yang, D, Zhu, R, Ge, F., Zhu, J. X., He, H., Removal of hexavalent chromium [Cr(VI)] from aqueous solutions by the diatomite-supported/unsupported magnetite nanoparticles, J. Hazard. Mater., 173, 614-21, (2010)), and can be used as a solute in a purification or desalination plant using osmosis due to water retention properties (Ling, M. M., Wang, K. Y., Chung, T.-S., Highly water-soluble magnetic nanoparticles as novel draw solutes in forward osmosis for water reuse, Ind. Eng. Chem. Res., 49, 5869-76 (2010)).
The magnetite nanoparticles having the above-mentioned properties can be prepared by various methods such as coprecipitation, thermal decomposition, micro-emulsion, hydrothermal synthesis, etc. (Lu, An-Hui, Salabas, E. L., Sch, Ferdi, Magnetic nanoparticles: Synthesis, protection, functionalization, and application, Angew. Chem. Int. Ed., 46, 1222-44 (2007)). Among them, according to the coprecipitation, the magnetite nanoparticles are prepared by dissolving an iron salt in water and allowing the solution to react at a relatively low temperature and at atmospheric pressure for several tens of minutes. Therefore, the coprecipitation is economic and suitable for mass production. Researchers have extensively studied various methods for preparing magnetite nanoparticles using the coprecipitation and, as an example thereof, a method for preparing a nanofluid, in which magnetite nanoparticles are prepared by coprecipitation and stably dispersed in a dispersion medium, has been developed (U.S. Pat. No. 3,843,540; Massart, R., Preparation of aqueous magnetic liquids in alkaline and acidic media, IEEE Trans. Magnetics MAG-17 (2), 1247-8 (1981)). Recently, Iwasaki et al. have developed a method for preparing magnetite nanoparticles at room temperature using various iron salts by coprecipitation (Iwasaki, T., Mizutani, N., Watano, S., Yanagida, T., Kawai, T., Size control of magnetite nanoparticles by organic solvent-free chemical coprecipitation at room temperature, J. Exp. Nanosci., 5, 25162 (2010)). Moreover, Korean Patent No. 10-442541 discloses a method for preparing magnetite nanoparticles using a ferrous sulfate salt by precipitation with multiple steps.
Commercially available high-purity iron salts such as FeCl2, FeCl3, Fe(CH3COO)2, Fe(CO)5, etc. have been used as starting materials in the preparation of magnetite nanoparticles in the conventional methods including the above-mentioned literatures. However, the high-purity iron salts are expensive, which is problematic.
Even if the expensive high-purity raw materials are used in industrial fields such as magnetic resonance imaging (MRI) contrast agents, catalysts, dust-proof seals, etc., the added value of the final product is high, which can sustain economic feasibility. However, in industrial fields such as wastewater treatment or desalination plants, the economic feasibility can be achieved when the cost of the raw materials is reduced. Moreover, in the industrial fields such as wastewater treatment or desalination plants, the amount of water to be treated is significant, and thus the demand for magnetite nanoparticles is significant. Therefore, in order to apply the magnetite nanoparticles in the industrial fields such as wastewater or desalination plants, it is necessary to develop a plan to reduce the cost of magnetite nanoparticles.
In order to solve the above-described problems, many researchers have extensively studied various methods for preparing high-purity iron salts from low-grade ores. As an example thereof, Korean Patent No. 10-905403 and U.S. Pat. No. 7,550,618 disclose a preparation of iron (II) acetate powder from low-grade magnetite. However, the process of preparing a nano-material by synthesizing a high-purity iron salt such as iron (II) acetate, iron chloride, etc. from low-grade iron ore and using the iron salt as a starting material is complex and costly.
Moreover, Korean Patent No. 10-1109682 discloses a method for preparing magnetite nanoparticles from low-grade iron ore. According to this method, magnetite nanoparticles were prepared from precipitated iron hydroxide obtained by removing impurities contained in iron ore leachate by polymer adsorption or coprecipitation without preparing high-purity iron salts such as iron acetate, etc. However, this method involves high processing costs due to a process of inducing precipitation by adding an alkaline neutralizing agent, a process of redissolving iron hydroxide with a strong acid, etc. Moreover, the nanoparticles prepared by this method have a purity lower than that of a sample prepared using a commercially available high-purity reagent, which causes deterioration of material properties such as magnetic properties, and thus cannot be used as materials for high-tech products that require a purity of more than 99%.
Therefore, it is necessary to provide a simplified process which can prepare magnetite nanoparticles directly from an inexpensive starting material without intermediate steps such as the synthesis of an iron salt or the precipitation of iron hydroxides, etc.